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Non-hydrostatic high pressure X-ray diffraction is used to study the hardness of superhard ReB₂nanocrystals. All nanocrystals show less plastic deformation under load than bulk ReB₂, with the smallest nanocrystals showing the most enhancement. 

Alloys of tungsten tetraboride (WB4) with the addition of C and Si were prepared by arc-melting of the constituent elements. The phase purity was established by powder X-ray diffraction (PXRD) and surface morphology by scanning electron microscopy (SEM) analysis. Vickers hardness measurements showed hardness enhancement for alloys with a nominal composition of (W0.98Si0.02):11.6B and (W0.95C0.05):11.6B of 52.2 ± 3.0 and 50.5 ± 2.5 GPa, respectively, compared to 41.2 ± 1.4 GPa for pure WB4. (W0.92Zr0.08):11.6B was determined in previous work to have a hardness of 55.9 ± 2.8 GPa. Bulk moduli were calculated following analysis of high-pressure radial diffraction data and were determined to be 329 ± 4 (K0′ = 2) and 390 ± 9 (K0′ = 0.6) GPa for 8 atom % Zr and 5 atom % C-doping, respectively, compared to 326–339 GPa for pure WB4. Computational analysis was used to determine the dopant positions in the crystal structure, and it was found that Zr primarily substitutes W in the 2c position, Si substitutes for the entire B3 trimers, and C inserts in the Bhex-layer. The hardness enhancement in the case of Zr-doping is attributed primarily to extrinsic hardness effects (nanograin morphology), in the case of C─to intrinsic effects (interlayer bond strengthening), and in the intermediate case of Si─to both intrinsic and extrinsic effects (bond strengthening and fine surface morphology). 

We report our discovery of utilizing perhydroxylated dodecaborate clusters ([B 12 (OH) 12 ] 2− ) as a molecular cross-linker to generate a hybrid tungsten oxide material. The reaction of [N n Bu 4 ] 2 [B 12 (OH) 12 ] with WCl 6 , followed by subsequent annealing of the product at 500 °C in air successfully produces a tungsten oxide material cross-linked with B 12 -based clusters. The comprehensive structural study of the produced hybrid material confirms a cross-linked network of intact boron-rich clusters and tungsten oxides. We further demonstrate how these robust B 12 -based clusters in the resulting hybrid tungsten oxide material can effectively preserve the specific capacitance up to 4000 cycles and reduce the charge transfer resistance as well as the response time compared to that of pristine tungsten oxide. Ultimately, this work highlights a promising capability of boron-rich clusters in hybrid metal oxides to obtain fast and stable supercapacitors with high capacitance.